Storage: Doesn't matter you are buying an ice cube tray or mold, the first thing you must consider is the storage of capacity of it. Ice cube molds or trays are of no use if they don't contain enough storage according to your necessity. So, make sure that the one you have chosen is perfect for your house.
Leak proof: The tray or must be leak proof. As water stays in liquid, so it is obvious that a leak in your tray is not going get you what you have bought the ice tray for. So, buy an ice tray or mold that is not going to leak right after a few days you've bought them.
Free of odor: There are a lot more other things that you need to keep in the freezer. Like meat, fish etc. If you have an ice tray with no cover then there is a higher possibility of the ice cube may smell as the other items within the freezer. So, it is better to buy an ice cube or mold that contains an upper cover with a view to keep your ice cubes free of odor.
Ease of cleaning: Nobody likes an ice cube tray or mold that is difficult to clean. So, try to choose such ice tray that will be easy to clean.